Commonly assigned U.S. Pat. No. 5,626,191 issued May 6, 1997 (hereinafter the '191 patent) discloses an in situ combustion processes for producing hydrocarbon from an underground hydrocarbon reservoir utilizing (i) at least one injection well placed relatively high in an oil reservoir for injecting an oxidizing gas into the hydrocarbon formation, and (ii) a production well for producing liquefied or gasified hydrocarbon from the hydrocarbon reservoir. The production well has a vertical section which is in communication with a horizontal leg extending substantially perpendicularly outwardly from the vertical section and having a “toe” portion and a “heel” portion. The horizontal leg is completed relatively low in the reservoir, and at a “heel” portion thereof is in communication with the vertical section. Air, or other oxidizing gas, such as oxygen-enriched air, is injected through the injection well into the hydrocarbon reservoir, typically via perforations in the upper part of a vertical injection well, located in the vicinity of the “toe” of the horizontal leg of the production well. The horizontal leg of the production well is oriented generally perpendicularly to a generally quasi-vertical combustion front of combusting hydrocarbon which is produced upon ignition of a portion of the hydrocarbon in the reservoir proximate the injection well. Such combustion front is supplied with oxidizing gas via the injection well. The “toe” of the horizontal leg portion is positioned in the path of the advancing combustion front. The resulting combustion front propagates from the “toe” of the horizontal leg along the horizontal leg in the direction of and towards the “heel” portion. During this process heated hydrocarbon in the reservoir in advance of the moving combustion front becomes liquefied or gasified and flows into the horizontal leg, and from such leg thereafter removed to the surface via the vertical section of the production well. This process of U.S. Pat. No. 5,626,191 is called “THAI™”, an acronym for “toe-to-heel air injection”, and a registered trademark of Archon Technologies Ltd., a subsidiary of Petrobank Energy and Resources Ltd, Calgary, Alberta, Canada.
U.S. Pat. No. 6,412,557, also commonly assigned, discloses a similar but modified process having the added step of placing a hydrocarbon upgrading catalyst along, within, or around the horizontal leg to substantially decrease the viscosity of the hydrocarbon and upgrade the quality of the hydrocarbon and increasing the flow of hydrocarbon from the reservoir into the horizontal leg of the production well for subsequent removal to surface. Such modified process is known in the industry by the trademark CAPRI™, likewise a registered trademark of Archon Technologies Ltd.
WO2005121504 (PCT/CA2005/000833) published Dec. 12, 2005, also commonly assigned, teaches a similar process to that of THAI™, further comprising the additional step of providing injection tubing inside the production well within the vertical section and substantially along the length of the horizontal leg to a position proximate the “toe” thereof, for the purpose of injecting a non-oxidizing medium comprising steam, water, or a non-oxidizing gas via said tubing to the “toe” region of said horizontal leg. The injection of such non-oxidizing medium into the “toe” region of the horizontal leg has the effect of displacing any oxidizing gas in such area and thus preventing combustion of upgraded hydrocarbon which has flowed into the horizontal leg, and further increases the ambient pressure in the horizontal leg so as to prevent or reduce further inflow of oxidizing gas from the injection well which is injecting oxidizing gas into the hydrocarbon reservoir.
Disadvantageously, in each of the above prior art methods for recovering liquefied and/or gasified hydrocarbons from a hydrocarbon formation oxidizing gas is needed to be injected proximate the toe of the horizontal leg, and remote from the vertical section of the production well. Such site of injection of oxidizing gas is remote from the vertical section of the production well, the surface of the production well being the location where oxidizing gas is typically generated. The injection and vertical section of the production wells can be separated by one (1) kilometer or more. Thus such prior art methods thus typically require transport of the oxidizing gas to the site of the injection well via piping from the production well, or alternatively require installation of equipment at the injection well site to permit generation of oxidizing gases for subsequent injection. Such requires clear access, via clearcutting, and/or increased space at the injection well site to accommodate additional oxidizing gas delivery and/or generation and compression facilities, thereby increasing the environmental “footprint” and impact of drilling operations on the environment, and also typically results in increased cost.
Thus a need thus exists for a modified process of THAI™ and CAPRI™ wherein such drawbacks are eliminated.